In the past, automotive light sources chiefly used incandescent bulbs. While working well and being inexpensive, these bulbs have a relatively short life and, of course, the thin filament employed was subject to breakage due to vibration.
Light emitting diodes (LEDs) have been proposed for lamps and automotive applications. These solid-state light sources have long lives and are not as subject to vibration failures. In order to replace an incandescent bulb with an LED light source, the LED light sources should function the same in the existing lamp assemblies and optics. For example, the LED light sources should have approximately the same light output and cannot exceed the electrical power consumption. In some applications, the lighting system (e.g., a turn signal) may require a minimum power consumption in order to work properly. Some flashers used with turn signals may require a minimum current in order to have the correct flash rate. If the current is below the threshold (e.g., in many LED based light sources), the flash rate goes up as if the bulb was burned out. The extra load may cause a significantly higher thermal load, and while LEDs may generate less heat compared to incandescent light bulbs, LEDs nevertheless do generate heat whose dissipation should be managed in order to control the junction temperature. A higher junction temperature generally correlates to lower light output and lower luminaire efficiency. Unfortunately, it may be difficult to dissipate thermal energy in many applications due to space constraints, for example, within the constraints of many lamp assemblies. Proposals for LEDs in automotive applications include those in U.S. Pat. No. 7,290,910 (Hohl-AbiChedid); U.S. Pat. No. 7,261,437 (Coushaine); U.S. Pat. No. 7,207,695 (Coushaine); U.S. Pat. No. 7,111,972 (Coushaine); U.S. Pat. No. 6,773,138 (Coushaine); U.S. Pat. No. 7,261,451 (Coushaine); U.S. Pat. No. 7,008,096 (Coushaine); and U.S. Pat. No. 6,682,211 (English). The following are also known: U.S. Pat. No. 5,160,200 (Cheselske); U.S. Pat. No. 6,371,636 (Wesson); U.S. Pat. No. 6,786,625 (Wesson); U.S. Pat. No. 7,407,304 (Tasson); and Pat. Pub. US 2003/0227774 (Martin).